XMods gearing chart
 

http://users.adelphia.net/~neurokinetik/gearing.png

Here's a quick gear ratio chart for XMods. Note that it is possible to shim the motor mount in order to use a larger pinion with a different idler gear. The ratios shown in red are combinations that cannot be done without shaving down the motor mount posts to allow the motor to sit low enough for the pinion and idler to mesh properly. Due to driveshaft clearance, this may not even work, so consider those ratios invalid. I have also included ratios for larger pinions, should acceptable gears be found.

Thanks for another informative post nuerokinetik.